Cascade systems which are used to recharge compressed gas cylinders, such as that of a Fire Fighters SCBA (self contained breathing apparatus) cylinder, Divers SCUBA (self contained underwater breathing apparatus) or paint ball gun compress gas cylinder(s), are comprised of one or more bank(s) of compressed gas storage cylinders connected to a flow control panel with valves. The compressed gas storage cylinder valves are opened or closed to permit the compressed gas flow from the individual storage cylinder(s) “banks” or “stages” into the SCBA/SCUBA cylinder(s).
Sequence cascading the flow from the various individual storage cylinders beginning with the lowest pressure cylinder 1st then progressing to the next highest pressure cylinder will maximize the total number of compressed gas cylinders which can be recharged. These cascade systems can also be equipped with accessory items such as compressor(s), which are used to refill the storage cylinders, and/or containment fill enclosure(s) to protect the operator from injury in the event of a cylinder rupture while it is being recharged.
At the present time, there are two basic types of cascade systems control/fill panels available which are used for recharging compressed gas cylinders. The first is a manually operated cascade control/fill panel. The second is an automatic sequencing cascade (auto-cascade) control/fill panel.
Manually Operated Control Panel:
The basic operation of a manual cascade fill panel used to recharge a high pressure gas cylinder is relatively simple. One or more high pressure compressed gas cylinder(s) which needs to be recharged are connected to the cascade system on the downstream side of the control panel while the high pressure compressed gas storage cylinder(s) are connected upstream of the control panel. The various cascade storage cylinders (stages) are connected to manually operated valves within the cascade control panel. The downstream sides of these manual valves are connected together in such a way as to permit the discharge exiting any manual valve(s) to be transferred into the cylinder which is being recharged.
The fill panel operator first compares the pressure of the cylinder(s) which are being recharged to that of the storage cylinders stages. The operator then opens the panel valve to the storage cylinder which has the pressure differential which is closest to, but higher than that of the cylinder(s) which are being recharged. This will permit the compressed gas from this particular storage cylinder/stage to flow into the cylinder which is being recharged. When the pressure in the cylinder which is being recharged equalizes with that of the storage cylinder, the operator closes this valve. The operator then opens the next higher pressure storage cylinder control panel valve which will then permit the compressed gas from this storage cylinder/stage to flow into the cylinder(s) which are being recharged. This process will continue until the cylinder being recharged reaches its maximum designed working pressure or equalizes pressure with that of the highest pressure storage cylinder/stage. The manually controlled cascade system is a good system but requires extensive training to use and the operator must pay close attention during its use to maximize the fill potential available within the storage cylinders. Any deviation of the above listed procedure will greatly diminish that maximum fill potential of the cascade system.
Automatically Sequencing Control Panel:
The second type of cascade system is the auto-cascade fill panel. This system is very easy for an untrained operator to use. Also, this system does not require the constant attention by the operator. Once the operator initiates the fill sequence, the auto-cascade system will then control the fill sequence until the cylinder which is being recharged reaches it's designed working pressure, equalizes with the highest pressure storage cylinder/stage or is stopped by the operator.
At the present time two types of auto-cascade fill panels available. Both types operate using the same principle of monitoring the pressures between the individual compressed gas storage cylinder(s) (banks) and that of the cylinder which is being recharged. As the pressure differentials between the cylinder(s) being recharged and individual compressed gas storage cylinder near equalization, either a pneumatic, hydraulic or electric valve is automatically opened to permit gas to flow from the next higher pressure compressed gas storage cylinder to flow into the cylinder which is being recharged.
Auto-Cascade Method #1
The 1st auto-cascade method/devise is a mechanical/pneumatic system. The various physical pressures within the system are transferred through tubing to one or more sequencing valves. The sequencing valve is comprised of two parts. The first part is a mechanically actuated high pressure on/off valve. The second part is a pressure differential valve which is to the top of the first valve. The following example demonstrates the operation of a 2-stage auto-cascade system.
A sequence valve is placed on the 2nd stage (compressed gas storage cylinders) of the system. The pressure from the 1st stage storage cylinder will be transmitted to one side of the differential pressure valve which is installed on the 2nd stage storage cylinder. The pressure from the cylinder being recharged is transferred to the second side of this differential pressure valve. As long as the pressure differential on either side of this valve is above a predetermined psi, the mechanically activated on/off part of the sequence valve will remain closed thus permitting only the gas from the 1st stage compressed gas storage cylinders to be transferred into the cylinder which is being recharged.
When the pressure in the cylinder which is being recharged nears equalization with that of the 1st stage storage cylinder, the pressure differential valve, with the assistance of a bias pressure spring, will cause the differential valve piston to move downward toward the second on/off section of the sequence valve assembly. This mechanical movement will open the on/off valve section of the sequence valve of 2nd stage storage cylinder thus allowing gas from the 2nd stage storage cylinder to begin to flow into the cylinder which is being recharged.
This sequence will continue until: 1—The operator stops the fill process. 2—The pressure of the cylinder which is being recharged equalizes with that of the highest pressure storage cylinder. 3—The cylinder which is being recharged reaches its maximum rated working pressure.
Auto-Cascade Method #2
The 2nd Auto-Cascade method/devise functions the same as the first method with one major exception. The pressure differential (sequence) valve(s) have been replaced with electric, electric over hydraulic or electric over pneumatic solenoid valve(s) and a computer, programmable logic circuit or peripheral interface controller which receives cascade system pressure information via electrical pressure transducers. The pressure transducers, which are located in various key areas of the system, electrically transmit pressure information to the computer or logic circuit. The computer or logic circuit program compares the pressure differential and then controls the discharge sequence of the compressed gas storage cylinder(s) into the cylinder(s) which are being recharged by opening electric, electric over pneumatic or electric over hydraulic solenoid valve(s) in the correct sequence and time as dictated by the pressure differentials.
While the above mentioned manual and automatic cascade systems function well, there are problems inherent to both designs.
Manual Cascade Problems
The single most common problem with a manual cascade panel operation is the opening of a cascade system panel “Stage” block valve prematurely. This will lower the pressure in that specific stage. The premature discharge and subsequent decrease in the pressure of this stage will have a catastrophic effect on the overall system efficiency and reduce the number of available cylinder recharges.
Pressure Differential Auto-Cascade Problems
The Pressure Differential based pneumatic auto-cascade system requires extensive tubing/plumbing to operate correctly. The complexity of this tubing/plumbing is costly to produce and prone to compressed gas leaks due to the numerous pipe/tubing connections which are required.
The Pressure Differential based electrical pressure transducer auto-cascade system requires the use of multiple pressure transducers, complicated wiring and sophisticated electronics, such as computer or PLC circuits to monitor pressures and control the compressed gas storage cylinder (stage) discharge sequence. This design is also costly to produce and prone to compressed gas leaks due to the numerous transducers to tubing connections which are required